git: 072901b7bc0b - stable/13 - sctp: Fix races around sctp_inpcb_free()
Mark Johnston
markj at FreeBSD.org
Tue Sep 14 12:52:14 UTC 2021
The branch stable/13 has been updated by markj:
URL: https://cgit.FreeBSD.org/src/commit/?id=072901b7bc0be6375940d06bf9e2fdce54a77a8e
commit 072901b7bc0be6375940d06bf9e2fdce54a77a8e
Author: Mark Johnston <markj at FreeBSD.org>
AuthorDate: 2021-09-07 13:44:12 +0000
Commit: Mark Johnston <markj at FreeBSD.org>
CommitDate: 2021-09-14 12:51:35 +0000
sctp: Fix races around sctp_inpcb_free()
sctp_close() and sctp_abort() disassociate the PCB from its socket.
As a part of this, they attempt to free the PCB, which may end up
lingering. Fix some bugs in this area:
- For some reason, sctp_close() and sctp_abort() set
SCTP_PCB_FLAGS_SOCKET_GONE using an atomic compare-and-set without the
PCB lock held. This is racy since sctp_flags is normally updated
without atomics, using the PCB lock to synchronize. So, the update
can be lost, which can cause all sort of races with other SCTP
components which look for the _GONE flag. Fix the problem simply by
acquiring the PCB lock in order to set the flag. Note that we have to
drop and re-acquire the lock again in sctp_inpcb_free(), but I don't
see a good way around that for now. If it's a real problem, the _GONE
flag could be split out of sctp_flags and into a dedicated sctp_inpcb
field.
- In sctp_inpcb_free(), load sctp_socket after acquiring the PCB lock,
to avoid possible races with parallel sctp_inpcb_free() calls.
- Add an assertion sctp_inpcb_free() to verify that _ALLGONE is not set.
Reviewed by: tuexen
Sponsored by: The FreeBSD Foundation
(cherry picked from commit c17b531bedd10c7ebea08919fd73ee708ff37336)
---
sys/netinet/sctp_pcb.c | 16 ++++++----------
sys/netinet/sctp_usrreq.c | 31 +++++++++++--------------------
2 files changed, 17 insertions(+), 30 deletions(-)
diff --git a/sys/netinet/sctp_pcb.c b/sys/netinet/sctp_pcb.c
index 3e517889d171..85ea5a3f8a53 100644
--- a/sys/netinet/sctp_pcb.c
+++ b/sys/netinet/sctp_pcb.c
@@ -3321,19 +3321,15 @@ sctp_inpcb_free(struct sctp_inpcb *inp, int immediate, int from)
/* mark any iterators on the list or being processed */
sctp_iterator_inp_being_freed(inp);
SCTP_ITERATOR_UNLOCK();
- so = inp->sctp_socket;
- if (inp->sctp_flags & SCTP_PCB_FLAGS_SOCKET_ALLGONE) {
- /* been here before.. eeks.. get out of here */
- SCTP_PRINTF("This conflict in free SHOULD not be happening! from %d, imm %d\n", from, immediate);
-#ifdef SCTP_LOG_CLOSING
- sctp_log_closing(inp, NULL, 1);
-#endif
- return;
- }
+
SCTP_ASOC_CREATE_LOCK(inp);
SCTP_INP_INFO_WLOCK();
-
SCTP_INP_WLOCK(inp);
+ so = inp->sctp_socket;
+ KASSERT((inp->sctp_flags & SCTP_PCB_FLAGS_SOCKET_GONE) != 0,
+ ("%s: inp %p still has socket", __func__, inp));
+ KASSERT((inp->sctp_flags & SCTP_PCB_FLAGS_SOCKET_ALLGONE) == 0,
+ ("%s: double free of inp %p", __func__, inp));
if (from == SCTP_CALLED_AFTER_CMPSET_OFCLOSE) {
inp->sctp_flags &= ~SCTP_PCB_FLAGS_CLOSE_IP;
/* socket is gone, so no more wakeups allowed */
diff --git a/sys/netinet/sctp_usrreq.c b/sys/netinet/sctp_usrreq.c
index 822a8ffb534f..62d6996ab60d 100644
--- a/sys/netinet/sctp_usrreq.c
+++ b/sys/netinet/sctp_usrreq.c
@@ -416,24 +416,23 @@ sctp_abort(struct socket *so)
{
struct epoch_tracker et;
struct sctp_inpcb *inp;
- uint32_t flags;
inp = (struct sctp_inpcb *)so->so_pcb;
if (inp == NULL) {
return;
}
+ SCTP_INP_WLOCK(inp);
NET_EPOCH_ENTER(et);
-sctp_must_try_again:
- flags = inp->sctp_flags;
#ifdef SCTP_LOG_CLOSING
sctp_log_closing(inp, NULL, 17);
#endif
- if (((flags & SCTP_PCB_FLAGS_SOCKET_GONE) == 0) &&
- (atomic_cmpset_int(&inp->sctp_flags, flags, (flags | SCTP_PCB_FLAGS_SOCKET_GONE | SCTP_PCB_FLAGS_CLOSE_IP)))) {
+ if (((inp->sctp_flags & SCTP_PCB_FLAGS_SOCKET_GONE) == 0)) {
+ inp->sctp_flags |= SCTP_PCB_FLAGS_SOCKET_GONE | SCTP_PCB_FLAGS_CLOSE_IP;
#ifdef SCTP_LOG_CLOSING
sctp_log_closing(inp, NULL, 16);
#endif
+ SCTP_INP_WUNLOCK(inp);
sctp_inpcb_free(inp, SCTP_FREE_SHOULD_USE_ABORT,
SCTP_CALLED_AFTER_CMPSET_OFCLOSE);
SOCK_LOCK(so);
@@ -448,13 +447,9 @@ sctp_must_try_again:
so->so_pcb = NULL;
SOCK_UNLOCK(so);
} else {
- flags = inp->sctp_flags;
- if ((flags & SCTP_PCB_FLAGS_SOCKET_GONE) == 0) {
- goto sctp_must_try_again;
- }
+ SCTP_INP_WUNLOCK(inp);
}
NET_EPOCH_EXIT(et);
- return;
}
static int
@@ -516,7 +511,6 @@ sctp_close(struct socket *so)
{
struct epoch_tracker et;
struct sctp_inpcb *inp;
- uint32_t flags;
inp = (struct sctp_inpcb *)so->so_pcb;
if (inp == NULL)
@@ -525,25 +519,26 @@ sctp_close(struct socket *so)
/*
* Inform all the lower layer assoc that we are done.
*/
+ SCTP_INP_WLOCK(inp);
NET_EPOCH_ENTER(et);
-sctp_must_try_again:
- flags = inp->sctp_flags;
#ifdef SCTP_LOG_CLOSING
sctp_log_closing(inp, NULL, 17);
#endif
- if (((flags & SCTP_PCB_FLAGS_SOCKET_GONE) == 0) &&
- (atomic_cmpset_int(&inp->sctp_flags, flags, (flags | SCTP_PCB_FLAGS_SOCKET_GONE | SCTP_PCB_FLAGS_CLOSE_IP)))) {
+ if ((inp->sctp_flags & SCTP_PCB_FLAGS_SOCKET_GONE) == 0) {
+ inp->sctp_flags |= SCTP_PCB_FLAGS_SOCKET_GONE | SCTP_PCB_FLAGS_CLOSE_IP;
if (((so->so_options & SO_LINGER) && (so->so_linger == 0)) ||
(so->so_rcv.sb_cc > 0)) {
#ifdef SCTP_LOG_CLOSING
sctp_log_closing(inp, NULL, 13);
#endif
+ SCTP_INP_WUNLOCK(inp);
sctp_inpcb_free(inp, SCTP_FREE_SHOULD_USE_ABORT,
SCTP_CALLED_AFTER_CMPSET_OFCLOSE);
} else {
#ifdef SCTP_LOG_CLOSING
sctp_log_closing(inp, NULL, 14);
#endif
+ SCTP_INP_WUNLOCK(inp);
sctp_inpcb_free(inp, SCTP_FREE_SHOULD_USE_GRACEFUL_CLOSE,
SCTP_CALLED_AFTER_CMPSET_OFCLOSE);
}
@@ -563,13 +558,9 @@ sctp_must_try_again:
so->so_pcb = NULL;
SOCK_UNLOCK(so);
} else {
- flags = inp->sctp_flags;
- if ((flags & SCTP_PCB_FLAGS_SOCKET_GONE) == 0) {
- goto sctp_must_try_again;
- }
+ SCTP_INP_WUNLOCK(inp);
}
NET_EPOCH_EXIT(et);
- return;
}
int
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